The invention relates to a method and a device for measuring the angle of a rotatable body, in particular of a body rotatable by 360.degree..
In connection with various applications, in particular with arrangements with the aid of which the angular position of a rotatable shaft is to be determined, there is a desire to know the exact position of the shaft immediately following start-up of the arrangement. This requirement can be best met with the aid of analog angle sensors, for example potentiometers, which provide the valid angular position in the form of a voltage in every position following start-up.
When such arrangements for angular measuring are employed for angular ranges which are greater than 360.degree., the problem arises that it can no longer be determined in which revolution the shaft is. However, incremental sensors can be used for evaluating angular ranges which are greater than 360.degree., in which the angular position is determined by forward or backward counting of pulses. However, it is not possible to perform an absolute angle measurement with such incremental sensors, because it is only possible to count increments which move past a counter.
So that an angular measurement of angular ranges larger than 360.degree. is possible, it is proposed in not yet published German patent application DE-P 44 09 892 in connection with the detection of a steering angle of a motor vehicle, to perform the determination of the steering wheel angle, which extends over a range of .+-.720.degree., with the aid of a planetary gear system. In this case the number of teeth of the planetary gear system is dimensioned in such a way that a value of exactly 4 results for the gear ratio between the steering axle and the pick-up disk to be scanned. The pick-up disk to be scanned therefore only rotates once while the steering angle is changed by .+-.720.degree.. By means of applying a code to the pick-up disk and scanning it with a suitable sensor it is possible to determine the position of the pick-up disk immediately following start-up, and a steering wheel angle determination is also immediately possible with this.
This known arrangement for the angular measurement of angular ranges greater than 360.degree. has the disadvantage that an exactly dimensioned planetary gear system is necessary and that in addition an elaborate absolute sensor system is required.